This invention relates to a furnace lining. By xe2x80x9cfurnacexe2x80x9d we mean a furnace, kiln, oven or the like where there is a chamber which is heated, and into which articles are placed for heat treatment.
Furnaces tend to be dusty, particularly where there is provided a fan or high velocity burner or the like for circulating hot air within the furnace, and dust is undesirable, particularly in the case of a kiln in which ceramic articles/glazes are fired, or in an oven where vitreous enamel is baked dry. The problem of dust is aggravated where there is provided an insulating lining which is of a fibrous nature which may contain silica, which may also present a potential health hazard if the fibres become airborne.
To reduce the amount of dust contributed by the furnace lining it is common to cover the lining with a protective covering such as high-temperature resistant textile material which is attached to the lining e.g. by pins. Another approach is to cement anchors into the fibres of the insulating lining.
Yet another approach is to attach to the hot face of the lining, i.e. the face of the lining facing inwards of the furnace, ceramic plate-like members. This is used where the underlying lining requires protection from deleterious atmospheres, e.g. aggressive gases such as vanadium pentoxide which can eat away the fibrous lining material.
This latter approach provides the advantage that the ceramic plates, being generally rigid, may be used as supports for, for example, heating elements. Such ceramic plates are typically attached to the hot face with a cement material, but the adhesive effect of such cements tends to deteriorate in use with the effect that the ceramic plates separate from the insulating lining. It will be appreciated that a falling ceramic plate can cause substantial damage to articles in the kiln, particularly where the ceramic plate is attached to the lining of a roof of the kiln, and results in damage occurring to the lining.
More expensive furnace lining materials are known such as that sold under the name xe2x80x9cSaffilxe2x80x9d. These do not contain silica but are about 90% alumina based fibrous insulation. Another alternative is a glass based fibre such as xe2x80x9cSuperwoolxe2x80x9d.
As these do not contain silica, they are not subject to health and safety legislation controlling the use of silica based materials. Saffil is a more expensive furnace lining material than silica based materials and Superwool, and thus tends only to be used in environments where higher temperatures are experienced. Hence for economy""s sake, the furnace lining has to be designed with the temperature to which the furnace is to be heated in mind, and once designed there is, conventionally, little scope for improving the thermal resistance of the lining.
In some circumstances it is desirable to have a protective element at the cold face between the furnace wall and the furnace lining.
According to a first aspect of the invention we provide a lining for a furnace the lining having insulating material attached to an inside wall of the furnace, the insulating material in use having a hot face which faces inwardly of the furnace and a cold face at or adjacent the furnace wall, characterised in that a protective element is provided at least partially to cover the hot and/or the cold face, the protective element being secured relative to the face by a securing means which co-operates with a member which is embedded in the insulating material.
Thus particularly but not exclusively where the protective element is secured relative to the hot face of the insulating material the invention may provide the advantage of a conventional furnace lining which comprises a protective ceramic plate or plates attached to the hot face of the insulating material, but the manner by which the ceramic plate is attached is more secure than a simple cement attachment.
It is envisaged that a ceramic plate type protective element may be attached by both adhesive cement and the securing means/embedded member so that in the event that the cement fails, the co-operation between the securing means/embedded member will prevent the protective element becoming detached from the face of the insulating material, and vice versa.
Alternatively, the advantages of non-silica containing insulating materials may be provided by attaching one or more layers of non-silica containing material, e.g. in the form of a blanket, to a conventional silica-containing insulating material lining. Thus an existing lining may be adapted for use in higher temperature applications by applying a layer of Saffil or the like particularly to the hot face of the insulating material, as the higher grade, non-silica containing material is tolerant to higher surface temperatures.
Where the lining does not require upgrading but it is desired to provide a protective element to isolate the silica containing materials, a layer of Superwool or the like may be attached.
Where it is desired to do so, a layer or layers of conventional silica-containing lining materials may be added to the hot face of the insulating material of an existing lining structure, to upgrade the lining, although some means to protect the silica-containing lining materials from becoming airborne may be necessary to comply with health and safety legislation.
In one embodiment the securing means comprises a headed fastener a shank of which co-operates with the embedded member. For example, most conveniently the shank of the headed fastener has provided thereon, a screw thread, e.g. a male screw thread, and the embedded member includes a corresponding opposite screw thread, e.g. female threaded opening, with which the shank is in use engaged. Thus the fastener may be unscrewed for maintenance of the lining as and when required. However it is envisaged that the shank of the headed fastener may otherwise co-operate with the embedded member to attach the protective element at the respective face.
The shank of the threaded fastener may pass through a passage of the protective element into co-operation with the embedded member. For example, the passage may comprise a pre-formed opening through the protective element or a cut-out at a side of the protective element as desired.
Of course, in the construction of the first embodiment of the invention where the protective element is provided at the hot face, the headed fastener will be subjected to the heat within the furnace and so preferably the fastener is made at least substantially, and preferably totally, of a ceramic material. In low temperature environments though or at the cold face, the fastener could be made of, for example, nickel chrome or another suitable metal.
In another embodiment, the embedded member comprises an integral shank or is adapted to have a shank secured thereto, and the securing means is engageable with the shank to secure the protective element to the respective face.
Either the securing means or the shank may pass through the protective element for securing to the shank or the securing means respectively.
In each case, whether the protective element is secured to the hot or the cold face, because the securing means co-operates with the embedded member, there is no path for the conduction of heat from the hot to the cold face and hence to the inside furnace wall, via the securing means.
The protective element is preferably as light as possible and may conveniently be of plate-like configuration, made at least substantially and preferably totally, of a ceramic material. However, the protective element could comprise a blanket of silica free insulation such as Superwool or a high-temperature resistant textile material, and/or a higher temperature resistant high alumina insulation than other insulating material of the lining.
However, the protective element could comprise additional layers of the same insulating material as that from which the remainder of the lining is made.
Whether the protective element is provided at the hot and/or cold face a furnace lining typically includes a plurality of individual blocks or modules of insulating material, each attached at the inside wall of the furnace. For example, each module may comprises a ceramic blanket which is folded to a block-like shape, with the folds extending transversely to the furnace wall.
The member with which the fastener co-operates may be embedded in at least one of the individual blocks during manufacture of the block and may be arranged to as to extend generally transversely to the folds.
The embedded member may have an integral shank or may be adapted to have a shank secured thereto. In either case, instead of being embedded in the block during manufacture of the block, the embedded member may be embedded in the lining by being forced into the lining material and then being rotated.
For example the embedded member may be generally elongate or may have a generally elongate part or parts. Each block may comprise a ceramic blanket which is folded to a block-like shape, with the folds extending transversely to the furnace wall. The embedded member may be forced into the insulating material with an elongate axis thereof or of the elongate part in an orientation generally aligned with the folds and is then rotated generally about an axis which is transverse to the elongate axis so that the elongate axis extends generally transverse to the folds.
The embedded member may be thin e.g. of a single plate or multiple plate-like construction, and may be made substantially or totally of a ceramic material or another suitable material which is sufficiently strong to resist pull-out forces.
Whereas the protective element may comprise a single layer construction, the protective element may comprise a plurality of layers which may or may not be bonded together.
The protective element, or where the protective layer comprises single layers of e.g. ceramic, the protective element may additionally be secured relative to the hot or cold face by adhesive cement.
According to a second aspect of the invention we provide a lining for a furnace the lining including insulating material attached at an inside wall of the furnace, the insulating material in use having a hot face which faces inwardly of the furnace and a cold face at or adjacent the furnace wall, characterised in that a protective element is provided at least partially to cover the hot and/or the cold face, the protective element being secured relative to the face by means including a headed fastener, a shank of which co-operates with a member which is embedded in the insulating material.
According to a third aspect of the invention we provide a lining for a furnace having insulating material attached at an inside wall of the furnace, the insulating material in use having a hot face which faces inwardly of the furnace and a cold face at or adjacent the furnace wall, characterised in that a protective element is provided at least partially to cover the hot and/or the cold face, the protective element being secured relative to the face by means including a member which is embedded in the insulating material and a securing means which is attached to a shank which is integral with the embedded member or is attached to the embedded member, the shank or the securing means passing through the protective element into engagement with the embedded member or the securing means.
According to a fourth aspect of the invention we provide a method of lining a furnace wall comprising the steps of attaching insulating material to the wall of the furnace, the insulating material in use having a hot face which faces inwardly of the furnace and a cold face at or adjacent the furnace wall, characterised in that the method comprises embedding in the insulating material, a member which is adapted to co-operate with a securing means, providing a protective element at least partially to cover the hot and/or cold face, securing the protective element to the face by attaching the securing means to the embedded member.
Where the securing means comprises a headed fastener, the method may include inserting a shank of the headed fastener through the protective element into the insulating material so that the shank may co-operate with the embedded member.
The shank of the headed fastener may co-operate with the embedded member by rotating the shank relative to the embedded member so that a screw thread of the shank engages with a corresponding screw thread of the embedded member although other methods of co-operation may alternatively be employed.
In a typical furnace lining construction the insulating material is attached to the furnace wall by a fixing means which is operated on from the hot face of the material, using a tool which is passed through the insulating material in an opening from the hot face of the material. For example a self-drilling fastener of the fixing means may be driven into the furnace wall by being rotated using a tool which is inserted through the fibrous insulating material, thus creating an opening therethrough, and the tool is operated from the hot face of the insulating material. Alternatively, a fastener of a fixing means or the fixing means itself may be welded to the inside furnace wall, using a welding tool which is inserted through the fibres of the lining, thus creating an opening therethrough.
The method of the invention may include inserting the shank of the fastener through the opening into co-operation with the embedded member so that there is no need to provide an additional opening to receive the shank of the headed fastener.
Instead of the securing means comprising a headed fastener a shank of which co-operates with the embedded member, the embedded member may comprise an integral shank, or the method may include attaching a shank to the embedded member, and the method may include engaging the securing means and the shank to secure the protective element to the hot and/or the cold face.
The method may further include positioning the protective element at the hot or cold face of the insulating material and either passing the shank which is integral or attached to the embedded member through the protective element or passing the securing means through the protective element and engaging the securing means and the shank so that the protective element is retained between the securing means or a part thereof and the face.
The embedded member may be embedded in the insulating material during manufacture of the block or may be embedded in the insulating material by forcing the member into the insulating material and then rotating the member so that the member may cut or divide the insulating material and be anchored therein.
The furnace lining may be modular comprising a plurality of modules or blocks of insulating material, and the method may be characterised in that a substantial part of the furnace wall is covered by a plurality of protective elements each secured at the hot face of the insulating material at least one an individual module, by means including a securing means which co-operates with a member which is embedded in the insulating material.
Where the insulating material is formed with folds which extend transversely to the furnace wall, the method may include inserting the member to be embedded when in an orientation generally aligned with the folds so as to cause minimum disruption to the insulating material as the member is forced in, and then rotating the member so that the member extends transversely to the folds.
In one arrangement, the member to be embedded includes a shank and the member is rotated by using the shank as a tool, although alternatively the member may be rotated using a tool which co-operates with the member and is subsequently removed from the insulating material.
According to a fifth aspect of the invention we provide a method of lining a furnace wall comprising the steps of attaching insulating material to the wall of the furnace, the insulating material in use having a hot face which faces inwardly of the furnace and a cold face at or adjacent the face wall, characterised in that the method comprises embedding in the insulating material, a member which is adapted to co-operate with a shank of a headed fastener, providing a protective element at least partially to cover the hot or the cold face, securing the protective element to the face by inserting the shank of the headed fastener though the protective element into the insulating material, so that the shank may co-operate with the embedded member.
According to a sixth aspect of the invention we provide a method of lining a furnace wall comprising the steps of attaching insulating material to the wall of the furnace, the insulating material in use having a hot face which faces inwardly of the furnace and a cold face at or adjacent the furnace wall, characterised in that the method comprises embedding in the insulating material, a member which is adapted to co-operate with a securing means, providing a protective element at least partially to cover the hot or cold face, securing the protective element to the face by attaching the securing means to the embedded member such that the protective element is retained between the securing means or a part thereof, and the face.
At the hot face, at least where the protective element or elements are not cemented to the lining, it will be appreciated that by virtue of the protective element(s) being secured relative to the hot face by co-operation between the embedded member and the securing means, the protective elements may be removed subsequently to facilitate maintenance of the lining, such as the addition of layers required to repair mechanical and/or temperature damage to the lining.
Thus according to an seventh aspect of the invention we provide a method of repairing a lining of a furnace made by the method of the fourth, fifth or sixth aspects of the invention including the steps of removing the securing means, removing the protective element or a layer of the protective element, and securing a replacement protective element or protective element layer, to the face of the insulating material by a securing means which co-operates with a member which is embedded in the insulating material.
Where a furnace is lined with a lower grade insulating material and it is desired to improve either the thermal resistance of the lining or its tolerance of high temperature, this may readily be achieved either by replacing the protective element in use with a higher grade protective element where the invention is already employed, or adding one or more layers to the protective element, or the lining below the protective element.
According to an eight aspect of the invention we provide a method of improving the thermal resistance of an existing furnace lining having insulating material attached to an inside wall of the furnace, the insulating material in use having a hot face which faces inwardly of the furnace and a cold face at or adjacent a furnace wall and the insulating material having embedded thereon a member which is adapted to co-operate with a securing means the method being characterised in that a protective element is provided at least partially to cover the hot or cold face, the protective element being secured relative to the hot or cold face by the securing means co-operating with the member which is embedded in the insulating material.
Thus provided that an embedded member is provided in the insulating material of the lining, an existing lining may be upgraded with minimal disturbance of the lining.